I'm running mine at 3.6 (400x9) now. 1.28V vcore idle and 1.23V load. 4.0 (400x10)requires 1.40+ vcore (max vcore is 1.3625V according to Intel) in BIOS. Temps are good but I'm worried about the high vcore so I dropped it to 3.6. Didn't notice any performance difference in games running at 4.0 and 3.6.